The present invention is directed to methods of manufacturing soft tip catheters. In particular, the present invention is directed to a method of continuously manufacturing soft tip catheters.
Catheters are used during various surgical procedures for delivering solutions, probes or instruments to specific bodily areas. Depending upon the particular use, the catheter may have one or more internal lumens, or pathways through which the fluid or instrument is inserted. Generally, the catheter is pushed through a blood vessel until reaching the desired site by a twisting motion. In order to promote the ability of pushing the catheter through the blood vessels, the catheter should be rigid, while also possessing sufficient longitudinal flexibility. The combination of these two properties provides the catheter with a high degree of torsional control which allows for the twisting motion.
As the catheter is being pushed through the blood vessel it will come into contact with the vessel wall, and other body organs. The rigidity of the catheter, which is necessary to provide the torsional control, increases the potential of damaging the vessel wall or other body organ. This is particularly true for the catheter distal end, or tip, which may puncture, or in some other manner damage the vessel wall or body organ as the catheter is travelling through the blood vessel. In order to cure this problem catheters have been designed with soft or flexible distal tips to minimize the damage inflicted upon the vessel or organ as the catheter is being pushed through the blood vessel to the desired site.
An example of such a soft tip catheter is disclosed in U.S. Pat. No. 4,4O2,684, issued to Jessup. The catheter is formed with a soft outer sheath to define a single lumen. The desired rigidity of the catheter is provided by inserting a rigid stylete in the lumen.
This stylete may also be formed to subdivide the lumen into multiple lumens. The soft outer sheath surface minimizes the potential of damaging the blood vessel wall or body organ. The catheter is thus manufactured by first forming the outer sheath, and then by inserting the stylete into the lumen. This type of procedure does not lend itself to any type of automated manufacturing process.
Soft tip catheters are usually manufactured by fusing a flexible tubular portion to the distal end of a rigid catheter body. Examples of these types of catheters are disclosed in U.S. Pat. Nos. 4,563,181 issued to Wijayarathna et al; 3,485,234 and 3,585,7O7 both issued to Stevens; 4,321,226 issued to Markling; 4,531,943 issued to Van Tassel et al; and 4,665,604 issued to Dobowik. This type of catheter design is also disclosed in U.S. patent application Ser. No. 946,491, filed on Dec. 23, 1986, which is assigned to the same assignee of the instant application, the parent application of U.S. patent application Ser. No. 271,351, filed 11/10/88.
An example of one such fusing process is disclosed in Markling, Dubowik and Stevens, and is known as a lap joint fusing process. The various methods of fusing the soft tip to the distal end of a rigid catheter body, no matter what the specific process entails, does not lend itself to an automated process, and as a result is time and labor consuming.
Other methods of forming soft tip catheters have been developed whereby the catheter is formed with two sheaths, an inner sheath formed from a rigid material and an outer sheath formed from a more flexible material. The outer sheath is extended beyond the inner sheath to form an integral soft tip. Examples of such catheters, and the methods of forming the same are disclosed in U.S. Pat. Nos. 4,239,042, issued to Asai and 4,596,563, issued to Pande.
Another type of catheter construction is disclosed in U.S. Pat. No. 4,636,346 issued to Gold et al. This method involves forming a catheter from three sheaths, an inner sheath formed from polytetrafluoroethylene (PTFE), an intermediate sheath formed from a rigid polymeric material and an outer sheath formed from a more flexible polymeric material. The flexible tip portion is formed by eliminating that portion of the intermediate sheath contiguous to the distal portion of the catheter. Again, this is a complex manufacturing procedure which is time and labor intensive.
While the various discussed catheter construction methods provide adequate soft tip catheters, all suffer from the same disadvantage of being time and labor intensive. In particular, the discussed methods are not adaptable for use in an automated and continuous process.